Under circumstances where exploration activities are being conducted for petroleum products such as oil and natural gas, it is customary to drill deep wells from the surface of the earth to oil or gas bearing subsurface earth formations. Wells of this nature must be lined with large diameter pipe which is typically referred to as a well casing, which pipes are typically interconnected by means of threads. The wells are drilled by rotating a drill at the lower extremity of a drill string. The drill string is defined by a large number of interconnected drill pipe sections that are connected by means of threads. After the well has been drilled and production is in order, production tubing is introduced into the well which extends from a well head that is located at the surface and interconnected with the well casing. The production tubing is positioned within the casing and extends to one or more production zones intersected by the well bore. The tubing strings are defined by threaded joints of tubing that are connected in assembly.
During drilling operations and especially during production operations, it is likely that high pressure conditions may be encountered. It is necessary, therefore, that the threaded connections of the casing and tubing the capable of withstanding significantly high pressure differential without leaking. It is necessary, therefore, that the threads of the casing or tubing be in excellent, undamaged condition in order that leakage will not occur at the threaded joints. During drilling operations, the drill stem is typically subjected to extremely high internal pressure since drilling fluid is forced through the tubing string under high pressure generated by pumps of the well drilling equipment. The threads of the various joints of drill pipe are, therefore, required to be in excellent, undamaged condition in order to enable the drill string to withstand the internal pressure to which it is subjected.
Virtually all wells for petroleum products require large amounts of well casing, drilling pipe and production tubing. After manufacture of the pipe, it is typically handled a number of times before it actually reaches the drill site and is utilized during drilling or production installation. In handling the pipe, if the pipe threads are not protected, it is likely that the threads of the pipe will be damaged through contact with other objects. It is desirable, therefore, to provide the pipe with a thread protector structure that facilitates protection of the external threads of the pipe during the various handling operations that occur prior to installation or use of the pipe in a well.
The various pipe sections that are introduced into the well bore, whether well casing, drill pipe, production tubing, etc., are brought to the well site by trucks and are then off loaded onto horizontal pipe storage racks by means of hook and cable lifting apparatus. Hooks are inserted into each extremity of the pipe and a lifting cable, to which the hooks are assembled, is moved upwardly by a suitable lifting cable. Alternatively, the pipe sections may be simply rolled down a ramp from the truck bed to the pipe storage rack. Thread protectors and desirable to prevent the threads from becoming damaged during such handling.
When pipe is moved from the pipe storage rack to the drilling rig, a pipe receptacle is placed about the pipe and the pipe is moved end-wise to the rig. The trailing end of the pipe typically drags along a ramp to the rig. The thread protector must have sufficient wear resistant capability to withstand dragging of the pipe in this manner and yet provide protection against damage to the threads of the pipe.
Thread protectors are typically of quite inexpensive construction so that loss or damage thereof will not constitute a particularly adverse financial condition. It is required, however, that thread protectors be capable of withstanding severe blows at the pipe threads without allowing the threads to become damaged. In some cases, pipes thread protectors have been formed completely of plastic material such as in the case shown in U.S. Pat. No. 4,139,023 to Turley or combinations of plastic and metal material as set forth in U.S. Pat. No. 2,212,423 of Lytle. Thread protectors may be retained in assembly with the pipe structure by threaded connection as in the case of the Turley and Lytle patents or, in the alternative, may be retained by any other suitable interlocking mechanism such as shown by Kahn, et al in U.S. Pat. No. 2,156,221. Other thread protector patents of general interest to this subject matter include U.S. Pat. Nos. 1,974,546 of Shipley; 2,133,049 of Shimer; 2,213,430 of Irwin, et al; 2,580,762 of Grenier, et al and 2,824,579 of Groah, et al.